Fibrinogen is cleaved and polymerized into fibrin using thrombin in a well-characterized process. Thrombin cleaves fibrinogen, forming fibrin monomers. Once fibrinogen is cleaved, fibrin monomers come together and form a covalently crosslinked fibrin network in the presence of factors, such as Factor XIII, normally present in blood. At a wound site, the fibrin network helps to close the wound and promote healing.
Various attempts have been made to provide fibrin in a form useful for treating wounds. Perhaps the most commonly known is the in situ generation of fibrin glue, typically performed by delivering separate solutions of fibrinogen and thrombin from a dual-barrel syringe.
International Patent Publication No. WO 97/44015 (Heath et al.) purportedly describes soluble microparticles including fibrinogen or thrombin, in free-flowing form. It is stated that these microparticles can be mixed to give a dry powder, to be used as a fibrin sealant that is activated only at a wound site.
Attempts have been made to provide a pre-formed fibrin material as a wound covering. For example, U.S. Pat. No. 6,486,377 B2 (Rapp et al.) purportedly describes a biodegradable, flexible wound covering based on fibrin and a process for its preparation, in which a fibrinogen solution is subjected to a single-stage or multi-stage dialysis, then a flexible fibrin web is formed by action of a thrombin solution on the fibrinogen solution and this is subsequently subjected to freeze-drying.
In another attempt, International Patent Publication No. WO 2009/120433 A2 (Delmotte et al.) purportedly describes making a fibrin wound dressing by mixing quantities of fibrinogen solution and thrombin solution with air. According to publication, the resulting foam is very light weight, and with the proper attention to the amount of thrombin, will rest on a vertical surface without dripping. The wound dressing may also be formulated for its ability to continue migration of healing substances, such as PDGF, from the dressing to the wound site. Thrombin substitutes, such as other clotting proteins, may be used instead of thrombin. The resulting foam can purportedly be lyophilized or ground and lyophilized for later reconstitution.